Bolts having one or more unthreaded portions along their lengths are known per se. Typically the bolt has a plurality of alternate threaded and unthreaded portions along its shank, the purpose of the arrangement being to provide a fast-acting nut and bolt assembly, in the sense that sliding movement of the nut along an unthreaded portion of the bolt shank can take place rapidly and without rotation, so that fewer turns of the nut are required to tighten the nut at its desired operative position on the shank. In its tightened or clamping position the nut is threadedly engaged with the bolt as in conventional nut and bolt assemblies.
In accordance with the present invention the nut and bolt cooperate with each other such that in the clamping or holding position the nut resides at an unthreaded portion of the bolt shank and is not in threaded engagement with any portion of the bolt shank. The advantage of the arrangement is that the nut is less likely to unscrew during use of a joint formed by the nut and bolt assembly than is a conventional nut and bolt assembly. In the latter, any rotation of the nut in an unscrewing direction, as might occur during vibration, is accompanied by essentially immediate loosening of the nut, whereas in the arrangement according to the present invention rotation of the nut in an unscrewing direction does not result in unscrewing of the nut unless and until the nut becomes threadedly engaged with a threaded portion of the bolt shank. Typically, the nut in its operative position will be in axial compression, i.e. clamped tightly between the end of a threaded bolt portion and an element of one of the parts being held in position by the nut and bolt assembly. The invention does not exclude, however, the situation where the nut is relatively loose, in the sense that little or no axial compression is exerted on the nut in its operative or holding position.